1. Point source pollution: prevention and management Gordon Lethbridge, Environmental Section, HSE Consultancy Group, Shell Global Solutions, Cheshire Innovation Park, Chester, UK CH1 3SH

2. Overview of presentation • Groundwater protection strategies for large networks of sites • Groundwater protection strategies for large facilities • The role of risk assessment in groundwater protection • Groundwater protection measures • Industry – regulator partnerships • Conclusions

3. Prioritisation of sites in large networks: Network Environmental Risk Assessment (NERA) • GIS based desktop site prioritisation tool • Ranks sites in terms of potential environmental risk (SIV) • Groundwater usage, distance to abstraction wells, depth of abstraction, groundwater vulnerability • Not restricted to risks to groundwater • Ranks sites in terms of the condition of the assets (CIV) • Type and age of tanks and lines, corrosion prevention measures, corrosivity of soil • SIV and CIV can be integrated to get an overall assessment of potential risk • Process remains evergreen • Risk ranking may change over time as circumstances change

4. Site classification using NERA CIV Poor condition High risk C Low Risk A Medium risk B Good condition SIV Low sensitivity High sensitivity No action Priority action Monitor

5. Potential applications of NERA • Prioritise sites for investigation of soil and groundwater contamination • Prioritise sites for upgrading of facilities • Match containment and leak detection facilities to the level of risk posed by a site • Rapidly assess potential environmental liabilities of sites acquired from third parties • Identify any sites that pose an unacceptably high risk even with the most sophisticated containment and leak detection systems in place • Aid decision making in location of new sites

6. Examples of groundwater protection measures at retail filling station sites: containment • Double walled tanks • Double walled pipeline • Coated walls • Corrosion resistant materials in aggressive soils • Tank overfill protection • Provision of spill collection capacity at tank fill points • Leak proof pavement • Leak proof drainage system

7. Examples of groundwater protection measures at retail filling station sites: leak detection and monitoring • Wet stock management • Reconcile deliveries with sales and stocks • Monitor trends over time • Interstitial monitoring in double walled tanks and pipelines • External electronic leak detection • Groundwater monitoring

8. Groundwater protection at large facilities

9. Groundwater protection at large facilities • Risk-based product storage • Match products with tanks • High risk products in low risk tanks • Low risk products in high risk tanks • Risk-based approach to primary and secondary containment • Risk-based tank inspection • Inspect a high risk tank more frequently than a low risk one

10. Risks to groundwater from point sources: some observations • Major leaks and spills are very rare (emergency response) • Vast majority of leaks are minor. • Underground pipelines are a greater source of leaks than underground tanks • Problems with UST often due to sub-standard manufacture or poor installation technique • Spills can be minimised through use of appropriate technology and procedures

11. Groundwater protection following a spill or leak • Monitored Natural Attenuation (MNA) • Permeable reactive barriers • Source treatment / removal • Aggressive groundwater plume treatment

12. The life cycle of a BTEX plume in groundwater Red = contaminated groundwater Blue = clean groundwater 1. Expanding 2. Stable Time 3. Shrinking 4. Exhausted = source

13. 90% of BTEX plumes in groundwater are < 100 metres in length Based on 604 sites Source: API, 1998

14. Groundwater protection: industry – regulator partnerships • Recognition of need to develop solutions in partnership between the Environment Agencies and industry organisations such as SAGTA and Institute of Petroleum • Research projects • Workshops • Reciprocal review of technical guidance • Examples • Groundwater vulnerability at retail filling stations • MtBE in groundwater • Monitored Natural Attenuation

15. Conclusions • Risk assessment is the key to cost-effective groundwater protection • Large number of facilities requires site prioritisation • Match the level of containment, leak detection, inspection monitoring, SI and remediation to the level of risk posed by the site • When groundwater impacts do occur natural attenuation processes have great potential to mitigate risks • Industry – regulator partnerships are key to developing solutions which meet the needs of all parties